It is known from DE-PS 37 00 758 to connect rock anchors, drill rods and the like to one another by screw connections. For this purpose, in the known coupling, both drill rods or rock anchor parts to be connected to one another have an external thread and are connected to one another with a coupling or connecting sleeve that has a corresponding internal thread. The threads are usually round threads and are produced by forging a tube-shaped blank, and the internal thread of the sleeve is produced by an open deformation of the inside of the blank of the sleeve that corresponds to the deformation on the outside.
With such connections it is also known to limit the depth to which the tie rods can be screwed in by welding an annular disk into about the center of the coupling sleeve, an annular disk against which the tie rods lie on both sides with their front ends. This type of connection is disadvantageous to the extent that the tie rods lie adjacent to one another not directly but through the annular disk, so that in view of the high loads when being set down, especially during drilling and simultaneous boring of the injection drill bar, there are transmission losses.
From EP-A-391 119 is known a connecting element for a screw connection of automatic drilling injection anchors in which the internal thread of the coupling sleeve has two cylindrical parts lying at the ends and two bases going toward one another conically, lying about in the center of the sleeve, and on which the internal thread continues. This embodiment is disadvantageous since the tie rods, when they are screwed into the coupling sleeve, do not lie directly adjacent to one another and thus the forces occurring during drilling are only poorly transmitted.
It is known from U.S. Pat. No. 3,567,254 to provide the screwing-in depth of tie rods in coupling sleeves by a section of reduced diameter in the form of a torus (FIG. 4 of U.S. Pat. No. 3,567,254).
In the coupling for tie rods of (injection-) drilling anchors known from U.S. Pat. No. 3,567,254, a coupling sleeve is provided that has an internal thread into which the ends of tie rods that have an outer thread are screwed, and the tie rods with their end surfaces facing one another lie adjacent to one another all over.
From DE-A-14 83 840 is known a coupling for drill rods that are not hollow with the features of the introductory part of claim 1.
EP 187 628 A shows the measure of providing a bevel (tapered surface) on the exposed end of drill rods that have a threaded section at the end area. But these molded faces do not lie on the end of one of the two threaded sections in EP 187 628, so that an undefined status results.